Out of the blue my sbc began to ping slightly at mid throttle. Car has run fine all year and have never heard it before. Checked the timing and it is at 10 degrees initial and 34 all in at 3000 rpm. Always run premium fuel which in my area is 91 octane.
Any advice on what has changed would be helpful. I'm thinking maybe some bad fuel. Your thought are welcome and appreciated

No EGR on this engine. I just fueled it up and burned off a quarter tank playing with the timing and carb adjustment today to make sure it was set up right. I guess I will take it for an easy drive and burn off some fuel to see if it makes a difference.

Certainly wouldn't hurt to take a small sampling of your present fuel (perhaps enough to fill a small glass jelly jar about 1/2 way) and let it stand for a day or two, just for observation purposes. Also, a bit of carbon buildup can cause hotspots in the combustion chamber(s) and contribute to spark knock as well. Perhaps a "preventative" SeaFoam treatment might not be a bad idea as well.-Jim

Did some messing around last night after speaking to friend. He suggested moving the vacuum advance from ported to manifold vacuum, reset the timing to 12 degrees BTDC and take it for a run. Did as he suggested and the pinging has gone away. Whats up with that?
My friend is the one that built the engine so he is familiar with the set up. I had someone else do some tuning on it in the spring and they must have moved it from manifold vacuum to ported.
One thing i noticed after making the change is the engine seems to have lost some of its lopey idle......it seems smoother.

Chevy engines are supposed to use manifold vacuum. ported vacuum makes them lazy and sluggish. The idle is higher due to more advance. The manifold vacuum makes it have around 24 degrees advance at idle.

Chevy engines are supposed to use manifold vacuum. ported vacuum makes them lazy and sluggish. The idle is higher due to more advance. The manifold vacuum makes it have around 24 degrees advance at idle.

Is it commom for an engine to lose some of its lope at idle when switching to manifold vacuum vs. ported?

Out of the blue my sbc began to ping slightly at mid throttle. Car has run fine all year and have never heard it before. Checked the timing and it is at 10 degrees initial and 34 all in at 3000 rpm. Always run premium fuel which in my area is 91 octane.
Any advice on what has changed would be helpful. I'm thinking maybe some bad fuel. Your thought are welcome and appreciated

Beagle

Your probably seeing the change to winter time fuel. For cold weather starting they increase the amount top end high volatiles in the fuel. These are ping prone, so unless the weather turned cold at the same time the new winter fuel came out, your likely to get some ping.

I hear it in my headers, in Seattle they switched the mix a couple weeks ago, then the weather warmed up. When that combination happens, I can hear a light ringing sound off the headers when the engine is working hard that isn't there on summer mix fuels. When they switch back to summer mix in late April, early May that sound goes away. It's been like that for quite a few years.

That seems like a likely cause as well Bogie. All things being the same from a timing aspect etc.
I had it out today and it was 68 degrees and I could hear just the slightest ping. I don't imagine such a slight ping could do any damage.......could it?

I came across this thread and glad I did since I just moved my vacuum line to to manifold vacuum and yes, it did smooth the idle from the more lopey idle on my car as well. I am running a Summit Ready to Run dizzy and it has the 21 degree advance bushing installed in it and my initial timing is set at 14-15 degrees. I have no pinging thus far but it is too early to tell. The car starts fine when hot and I re-adjusted the carb and the idle. I admit that these things are a little fuzzy to me and I am trying to learn how they interact with one another. Everyday is a learning experience.

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